I feel like it'll have to be something where everything is controlled indirectly. I can't imagine how controls for a Mario Kart game in the usual style would work on any kind of mobile device, so unless they figure out some way around that, it'll probably end up being a game where you end up designing vehicles and building up your characters to win races.

I COULD however also see it as a real-time game if your vehicle moves automatically and all you're doing is holding the screen to drift at turns, but I just cannot see how that could be even remotely fun to play.

March seems like a pretty safe bet at this point, given that we know of no other new first party releases for Switch past Kirby: Star Allies (unless you're including games like Tropical Freeze, Nintendo LABO, or Fire Emblem which has never been shown)